1. Field of the Invention
The present invention relates, in general, to the storage and transport of compressed natural gas, and in particular, to a new and useful tank design for a refueling station for refueling vehicles using compressed natural gas (CNG).
2. Description of the Related Art
The following patents are relevant in the field of the present invention:
U.S. Pat. No. 5,351,726 entitled "System and Method For Compressing Natural Gas and For Refueling Motor Vehicles"; U.S. Pat. No. 5,211,021 entitled "Apparatus for Rapidly Filling Pressure Vessels With Gas"; U.S. Pat. No. 5,207,530 entitled "Underground Compressed Natural Gas Storage and Service System"; U.S. Pat. No. 4,987,932 entitled "Process and Apparatus for Rapidly Filling a Pressure Vessel With Gas"; U.S. Pat. No. 4,531,558 entitled "Gaseous Fuel Refueling Apparatus"; U.S. Pat. No. 5,350,442 entitled "Gas Handling System and Adsorbent Dryer Regeneration Apparatus"; U.S. Pat. No. 5,330,031 entitled "Alternative Fuel System For Powered Industrial Vehicle"; U.S. Pat. No. 5,315,831 entitled "Liquid Natural Gas and Compressed Natural Gas Total Fueling System"; U.S. Pat. No. 5,302,090 entitled "Method and Apparatus for the Utilization of the Energy Stored In a Gas Pipeline; U.S. Pat. No. 5,259,424 entitled "Method and Apparatus for Dispensing Natural Gas"; U.S. Pat. No. 5,327,730 entitled "Method and Apparatus for Liquifying Natural Gas For Fuel For Vehicles and Fuel Tank For Use Therewith; U.S. Pat. No. 5,238,030 entitled "Method and Apparatus for Dispensing Natural Gas; U.S. Pat. No. 5,253,682 entitled "Free Piston Gas Delivery Apparatus and Method"; U.S. Pat. No. 4,805,674 entitled "Natural Gas Storage and Retrieval System"; U.S. Pat. No. 4,749,384 entitled "Method and Apparatus for Quick Filling Gas Cylinders; and U.S. Pat. No. 4,501,253 entitled "On-Board Automotive Methane Compressor".
None of these patents disclose the specific arrangement and size of a refueling station tank designed according to the present invention.
The National Energy Policy Act of 1992 and the Clean Air Act Amendments of 1990 require fleet managers to purchase OEM vehicles or convert existing vehicles to run on alternative fuels. To help create demand, an increasing percentage of Federal and State-owned vehicles must be converted annually over the next five years to reduce dependence on foreign oil, and provide cleaner emissions.
Compressed Natural Gas (CNG) is the preferred alternative fuel in at least 35 states.
One of the most significant obstacles to increased use of alternative fuels is the lack of an infrastructure for refueling. Initial efforts are being placed on centrally housed and refueled fleets, such as those owned by government installations and industries such as utilities. Preference and significant tax incentives are given to establishing a network of privately operated refueling stations to allow wider use and acceptance of alternative fuel vehicles (AFVs). Federal and state government entities are encouraged to commit to refueling contracts with private firms to immediately provide a known level of demand.
With limited range, CNG AFVs are confined to "local" use. An expanded network of refueling stations will allow extended traveling range, and greater acceptance of CNG AFVs.
Initially, refueling stations consisted of a bank of Department of Transportation (DOT) cylinders. This soon gave way to use of a series of American Society of Mechanical Engineers (ASME) pressure vessels 16, 20, or 24 inches in diameter, and 16 to 30 feet long. Pressure is held at 5,000 psi at ambient temperature. (Pressure of the vehicle's tanks are 2,400, 3,000, or 3,600 psi.) Large installations call for storage of 40,000 to 60,000 standard cubic feet of CNG.
CNG can be stored in either bulk storage or cascade storage. Bulk storage is accomplished by either one large tank or several smaller tanks manifolded together. As CNG is drawn from the tank(s), all tanks draw down in pressure at the same rate.
Cascade storage provides more available CNG than does bulk storage for the same size containers. There are usually three or four banks of vessels in a cascade. A vehicle is fueled from the first bank. If there is insufficient CNG at the proper pressure in the first bank, the vehicle's tank is topped off successively from the second and subsequent banks. If necessary, the vehicle can be topped off directly from the compressor.